The present invention relates to the growing of foodstuffs in general and in particular to a method and apparatus for growing progressively higher trophic levels of marine life in a closed and ecologically balanced system.
Systemculture is a term coined to describe in a single word the essence of the present invention. It comprises multiple trophic levels and is a system of aquaculture which, unlike its predecessors, requires a continuous management of the interrelationship between the several trophic levels in the system.
While the trophic levels in a typical ecologically balanced food chain are many in number, they may be considered broadly in two categories. The two categories are plant life and plant-eating animals. Of principal interest presently is the growing of phytoplankton for food for oysters and clams and the collection of their effluent from the feeding for the growing of seaweed, which is harvested for providing a fertilizer or used as a food for omnivore -- e.g., lobster, shrimp, turtle, fish such as mahimahi, etc.
Heretofore, there have been, and indeed there are presently, two forms of well known aquacultures: a monoculture and a polyculture.
An example of a monoculture is the growing of seaweed and turtles in separate reservoirs. An example of a polyculture is the growing of turtles and seaweed together in the same reservoir. In the monoculture, the seaweed and turtles are fed nutrients and harvested for a market. This is analogous to the maintaining of cattle in a system feed lot wherein the cattle are maintained in an enclosure and feed, enriched with certain supplements, is transported to the cattle and fed to them in controlled amounts. In the polyculture, the turtles feed on the seaweed and in turn discharge wastes into the pond, which feeds the seaweed. Both the turtles and the seaweed are harvested as their respective volumes and numbers exceed the capacity of their enclosures.
In the monoculture there is a degree of management in that control is exercised over the amount of nutrients fed to the product to be marketed. There is, however, typically no attempt made to use the wastes and effluent of one to feed or otherwise produce the other.
In contrast, in a polyculture, the wastes and effluent of one trophic level are used to feed or otherwise produce the trophic level on which it feeds and, in a more sophisticated system, to feed or otherwise produce a higher trophic level. There is, however, no attempt made to control the amount of nutrients supplied by the one to the other, nor is there any control exercised over the manner in which the nutrients are supplied. The system is typically wholly contained and self-regulating.
While it is clear that a natural food chain is effective, it is equally clear to the point of being axiomatic that nature is not always the most efficient.
A principal object of the invention is, therefore, a system of growing seafood which is highly efficient.
The present invention, while applicable to the growing of multiple species of marine life, will be described principally with respect to the growing of shellfish, such as oysters, clams and lobsters, and the production of their nutrients.
Oysters, for example, feed most productively on certain species of phytoplankton. Phytoplankton is a small, microscopic, floating plant. It can't swim on its own. It is, in its natural state, when healthy, suspended in the sea. It grows, or possibly more correctly stated, multiplies by dividing. Its rate of growth or multiplication in nature is such that it reproduces about every 16 hours, depending on its species, the level of its nutrients and the temperature of its environment. The species of principal interest are Nitzchia sp., Thalassiosira pseudonana Skeletonema costatum, Phaeodactylum tricornutum, and Tetraselmis sp. Chaetoceras sp. Cryptomonas sp., Isochrysis sp. and Monochrysis sp. are good feed for larvae. The nutrients on which they depend in nature include nitrates, phosphates, silicates and trace elements. Dissolved oxygen, pH and ammonia levels must also be controlled and the temperature range within which they have their maximum growth rate is 24-26.degree. C. Temperatures within this range are typically found in the tropics. It is well known, however, that, while having an abundance of sunshine, the tropics are deficient in the nutrients necessary for oyster growth. They are deficient in nutrients because the nutrients are consumed rapidly and are not replenished quickly enough due to the high growth rates which prevail in the tropics, thus leaving to the colder climates the majority of the present oyster production, albeit at much slower growth rates.
At the present time, in the commercial shellfish industry, oysters are removed from the bottom of an oyster bed by dredging or tonging. Dredging is accomplished by scooping the oysters from the bottom of the oyster bed with mechanical shovels or by means of a vacuum. Tonging involves the use of long tongs which are manually manipulated by a person standing in a flat-bottom boat for grasping the oyster and raising them from the bottom of the oyster bed.
To prepare an oyster bed for the growing of oysters, oyster shells from a prior catch, or other clean surfaces, are laid on the oyster bed. When the seeds of the females have been fertilized by the sperm, the resulting larvae (spat), after a short period of random swimming about, attach (settle) themselves to the shells or other clean surfaces, undergo a metamorphosis and begin maturing as an oyster. Often a number of "spat" will "settle" on a single oyster shell. It will be understood that, if a number of oyster larvae attach themselves to the same clean surface, oyster clusters will form. The formation of oyster clusters makes it difficult during harvest to shuck the oysters and to sort them according to size. It is also hard to clean the mud and slit from the bottom of the oyster bed from the oysters if they are clustered.
Another method of growing oysters is called racking. In racking, oyster shells from a prior shucking are pierced and strung on strings. The strings are suspended from rods or the like forming racks in the ocean. Oyster spat is allowed to settle on the oyster shells attached to the strings. "Racking" of oysters shortens the growing period to market size of the oyster from approximately 3 years to 18 months, eliminates -- or at least reduces -- cleaning and avoids the time-consuming and costly inefficiencies of dredging and tonging. In racking, however, there are certain disadvantages which exist and which are commo to all present ocean-based commercial seafood growing operations. These are destructive weather, predation (sharks, etc.) pollution, problems of legal ownership, government regulations, the high cost of operation and, very importantly, lack of food control in terms of amunt, type and location relative to the location of the growing animals.
Land-based aquaculture eliminates many of the above mentioned problems and disadvantages inherent in traditional methods of fish farming. Moreover, the potential tonnage per hectare of a well organized land-based aquaculture is so high that great areas of ocean really aren't needed. Why aquatic efficiency is so great is not clearly understood. However, there are some reasons which may be accepted. First, production gets a boost from the aquatic relief of gravity and friction. To use an analogy, if a poultry farmer wants to cycle manure out to a field, grow grain there and bring the feed back, he must use shovels, wagons, spreaders, harvesters, storage bins and conveyor belts. The oyster farmer, using the method and apparatus of the present invention, only needs to lift a weir board and let the flow of water do the rest. A particle of effluent from an oyster at a site can be carried a mile down therunway to fertilize a cell of phytoplankton which, in turn, can be carried a mile back to be absorbed by another oyster.
Another factor in the aquatic efficiency is the structure and physiology of marine plants and animals. For example, seaweed can double its weight every 60 hours because all of its energy is going to growth and not to the stalk and stem that are needed for so much of the bulk of terrestrial plants.
Because of these factors, the clear need for an expanded world food production, and the ever increasing limitations on land production due to an ever decreasing availability of petroleum-based fertilizers and fuel-demanding irrigation, a number of individuals and companies have been conducting research on various forms of acquaculture and mariculture. Most of this research, however, has been based on relatively small-scale experiments under laboratory conditions. While there have been proposals, few entirely integrated large-scale, wholly land-based, commercially significant aquaculture systems have been attempted. For example, in U.S. Pat. No. 3,735,736 there is proposed a method and apparatus, using a system of trenches and the warm water effluent from a nuclear plant for growing shrimp. It is mentioned that the shrimp are fed periodically, but there is no discussion of how the food is produced, no disclosure of a method or means for producing the food continuously and no method or means disclosed for controlling the type of food, the amount of food delivered for feeding to a particular animal or small group of animals and the time of feeding.
To produce seafood in commercially significant quantities, it is considered essential that the nutrients for feeding the seafood be produced on a large scale in a controlled manner, and continuously. For example, to feed oysters, clams and the like, this means that large-scale algal ponds or reservoirs are required in which phytoplankton can be maintained in a state of "bloom" uninterruptedly for long periods of time, such as 30 to 60 days, and while a high percentage of its volume (such as one-half to two-thirds) is "harvested" continuously.
Heretofore, the largest man-made algal pond believed to have been attempted to be maintained for growing phytoplankton to feed seafood was about 12,000 gallons, or less than 1/8 acre in area and about 3 feet deep. So far as is known, however, there has been no report that the attempt was successful. If, indeed, the attempt was not successful, it would not be surprising, because large bodies of water are different from small bodies as a growing medium and heretofore were vastly more difficult to manage, especially when the management involved the maintenance of a large-scale continuous flow algal pond having a high density of phytoplankton, such as a density exceeding 10.sup.5 organisms/liter.